LED based illumination is at present more and more applied instead of conventional lighting such as halogen lights.
In general, LED based illumination applications comprise an LED fixture (e.g. comprising one or more LEDs) and an LED driver for powering the LED fixture. Such an LED driver, in general, comprises a power converter (e.g. a switched mode power converter such as a Buck or Boost converter) and a control unit controlling the power converter and thus the current as supplied to the LED fixture. The power converter of an LED driver for LED based applications is often operated at a comparatively high switching frequency (˜100 kHz or more) and provides as such a substantially continuous current to the LED fixture. However, a more efficient way to supply a current to an LED fixture may be to operate the power converter of the LED driver in a so-called boundary conduction mode (also known as critical condition mode) whereby a switch of the power converter is switched off at a predetermined level (e.g. determined from a set-point indicating a desired illumination characteristic), and switched on again at a zero-crossing of the current. Such an operating mode is e.g. described in US 2007/0267978. By operating the power converter in a critical conduction mode, less dissipation occurs in the switch or switches of the power converter, providing an improved overall efficiency. In order to determine at which current level the power converter is operating, the LED drivers as known in the art are provided with several current or voltage sensors providing feedback signals to a control circuit controlling the power converter. Such sensors in general provide their feedback signals to a plurality of input terminals of the control unit thus putting constraints to the complexity of the control unit or limiting the functionality of the control unit. As typically such control units are bought as separate components whereby only a limited number of configurations are available (e.g. with respect to the available in- or outputs), such a sensor feedback requirement may limit the choice of selecting a general purpose control unit or may require purchasing a more extended, thus more expensive control unit.